National Geographic Channel unlocks the secrets of revolutionary structures in a new series of Ancient Megastructures. Certain landmarks have captured the imagination and awe of modern-day architects and engineers around the world as they work to solve the mystery of how their ancient forebears were able to construct such beautiful, timeless and revolutionary structures with none of the machines and materials available to modern engineers. From the dreams that inspired them, to the blood and sweat that built them, discover the full story behind six magnificent structures that forever changed the landscape of architecture: Petra, Alhambra, St.Paul¿s Cathedral, Hagia Sophia, Machu Picchu and Angkor Wat.